title: Proteolytic cleavage in an endolysosomal compartment is required for activation of Toll-like receptor 9.
abstract: Toll-like receptors (TLRs) activate the innate immune system in response to pathogens. Here we show that TLR9 proteolytic cleavage is a prerequisite for TLR9 signaling. Inhibition of lysosomal proteolysis rendered TLR9 inactive. The carboxy-terminal fragment of TLR9 thus generated included a portion of the TLR9 ectodomain, as well as the transmembrane and cytoplasmic domains. This cleavage fragment bound to the TLR9 ligand CpG DNA and, when expressed in Tlr9(-/-) dendritic cells, restored CpG DNA-induced cytokine production. Although cathepsin L generated the requisite TLR9 cleavage products in a cell-free in vitro system, several proteases influenced TLR9 cleavage in intact cells. Lysosomal proteolysis thus contributes to innate immunity by facilitating specific cleavage of TLR9.
authors.affiliation: Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02115, USA.
authors.forename: Boyoun
authors.initials: B
authors.lastname: Park
authors.forename: Melanie M
authors.initials: MM
authors.lastname: Brinkmann
authors.forename: Eric
authors.initials: E
authors.lastname: Spooner
authors.forename: Clarissa C
authors.initials: CC
authors.lastname: Lee
authors.forename: You-Me
authors.initials: YM
authors.lastname: Kim
authors.forename: Hidde L
authors.initials: HL
authors.lastname: Ploegh
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002403:Cathepsins / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D018899:CpG Islands; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000276:immunology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D007113:Immunity, Innate / Q000502:physiology*; D047468:Immunoprecipitation; D008247:Lysosomes / Q000276:immunology / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D021381:Protein Transport / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D051217:Toll-Like Receptor 9; D002403:Cathepsins